Under many circumstances, it is desirable to separate particulate material out of suspensions so that the particulate material will not adversely affect equipment that acts on the suspensions. This is particularly true in the paper pulp making field, wherein the comminuted cellulosic fibrous material suspensions (paper pulp) oftentimes are contaminated by particles such as tramp metal, gravel, stones, nuts, knots, and inordinately large wood fiber bundles, or the like.
According to some known prior art procedures and apparatus for separating out such unwanted particles, an annular slot is defined through which the suspension must flow to get from the inlet to the outlet. The slot is dimensioned so that its smallest dimension is a dimension smaller than the smallest dimension of the particles to be separated out. Such devices typically are effective only at relatively low consistencies (e.g. up to about 3-4 percent), and are limited in the utility thereof to relatively larger particles for effective separation (that is the dimensions of the slot can be made only so small without excessive clogging).
According to a method and apparatus of the present invention, it is possible to practice effective separation of unwanted particles, such as tramp metal, stones, knots, etc., from paper pulp or a like suspension, even when the suspension is at medium consistency (i.e. between about 5-15 percent, and typically about 8-12 percent). Further, according to the present invention particles can be separated from the suspension even when the largest dimension thereof is significantly smaller than the smallest dimension of the slot or opening through which the suspension must flow.
According to one aspect of the present invention, an apparatus is provided for separating unwanted particles from suspensions. The apparatus comprises: means defining a generally annular-shaped opening between the inlet chamber and the outlet chamber, the means comprising an interior element and an exterior element, both disposed between the inlet chamber and the outlet chamber. And, rotating means disposed at the annular opening, the rotating means having a plurality of surface manifestation which span the annular opening, while allowing other portions of the annular opening to remain uncovered, so that as the rotating means rotates about an axis generally perpendicular to the plane containing the annular opening, particles are separated out from the suspension and pass to the separated-out particles outlet.
According to another aspect of the present invention, an apparatus is provided which comprises: a housing having a suspension inlet, a suspension outlet, and a separated-out particles outlet, and an interior chamber communicating with the suspension inlet and an interior chamber communicating with the suspension outlet; and a transition between the chambers. A rotatable shaft mounted for rotation with respect to the housing, the shaft including a disc thereon extending generally perpendicular to the axis of rotation of the shaft, the shaft mounted within the housing so that the disc is at the transition between the chambers. Means associated with the housing for defining, with the disc, an opening extending between the chambers. And, a rotatable element having a plurality of projections extending generally radially outwardly therefrom, the element mounted on the shaft, adjacent the disc, for rotation with the shaft, and the projecting elements extending so that extend over portions, but only portions, of the opening along the extent thereof.
By practicing the method according to the invention, it is possible to provide effective separation of unwanted particles from paper pulp suspensions even if the consistency thereof is between about 5-15 percent (typically about 8-12 percent) with enhanced effectiveness. The method according to the invention comprises the steps of: acting on the suspension as it is flowing from the inlet to the outlet through the opening so that particles having as the largest dimension thereof d', which is significantly smaller than d, are separated out from the suspension flowing to the suspension outlet, in addition to particles having as the largest dimension thereof a dimension equal to or greater than d. And, discharging the separated-out particles through the separated particles outlet. Also, the method may be practiced by causing the separated-out particles to move generally downwardly toward a container; causing a small upward flow of liquid, countercurrent to the separated-out particles flow, from the container, sufficient to prevent suspension from flowing into the container, while allowing particles that have been separated-out to flow into the container. And, periodically closing off the container and flushing all of the separated-out particles therefrom.
It is the primary object of the present invention to provide for the effective separation of undesired particles from a suspension inc1uding paper pulp suspensions having medium consistencies. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.